This invention is concerned with improvements in or relating to adhesive compositions free of volatile solvents.
In the field of adhesive compositions there is a persistent desire to provide adhesive compositions free of volatile solvents for various reasons. For example, volatile solvents commonly used in the adhesives trade are inflammable materials, and also some of them are regarded as undesirable or unsatisfactory for health reasons.
One approach to reduction in the amounts of volatile solvent used is to provide adhesive compositions in the form of aqueous dispersions or emulsions. Available compositions of this type are suitable for a variety of purposes where removal of the aqueous medium can be achieved without significant problems. For example, aqueous based adhesive compositions are known which comprise a dispersion of film forming resin (for example an acrylic copolymer) finely divided filler, tackifying substance and optionally thickeners and wetting agents. These known compositions have found application as flooring adhesives. While such adhesives perform their adhesive function satisfactorily, some contain minor amounts of volatile organic solvents, which become objectionable in the atmosphere when applied films of the adhesives are drying.
It is one of the various objects of this invention to provide an adhesive composition which is totally free of the more volatile organic solvents.
Adhesives for securing flooring materials for example PVC flooring materials are required to have a combination of properties to facilitate their use in so-called one way methods of bonding. These adhesive compositions are normally applied to a floor, and flooring material applied thereto. In the case of absorbant flooring materials, for example textiles, the flooring is usually applied to the layer of adhesive while the layer is wet, whereas in the case of nonporous flooring materials it is usual to allow the adhesive layer to dry out to a so called "semi-dry" condition in which the layer is pressure sensitive prior to application of the flooring material. Thus, the composition is required to be capable of application to the floor to provide a layer of adhesive in a desired pattern and to be capable of displaying adhesion to flooring material surfaces which may be pervious to water, and of displaying pressure sensitive properties to impervious substrates.
Resins used in aqueous dispersion adhesive compositions frequently have insufficient tack for pressure sensitive applications and require use of tackifying agents. However, in order to incorporate tackifying resins without generating instability of the composition it is usual practice to add them to the composition as a solution in low boiling organic solvents, which in turn gives rise to objections in relation to flammability, toxicity and/or odor. When it is desired to use no low boiling solvent whatsoever, one has to ensure that the tackifying substances used confer desired properties but do not lead to instability of the dispersion.